Integrated circuits contain millions of individual elements that are formed by patterning the materials, such as silicon, metal and/or dielectric layers, that make up each integrated circuit. A technique used throughout the industry for forming such patterns is photolithography.
A typical photolithography process sequence generally includes depositing one or more uniform photoresist (resist) layers on the surface of a substrate, drying and curing the deposited layers, patterning the substrate by exposing the photoresist layer to electromagnetic radiation that is suitable for modifying the exposed layer, and then developing the patterned photoresist layer.
Photolithography is an important process of wafer fabrication. In the photolithographic process, photoresist chemicals are dispensed on the wafer using high precision chemical dispensing pumps known as photoresist pumps.
A photoresist pump is desirably supplied with an undisturbed supply of photoresist to avoid air bubbles from going inside the pump. One approach is to supply the photoresist directly from a photoresist bottle 20 to the photoresist pump 30, as shown in FIG. 1.
There are several drawbacks to this approach. The photoresist bottle 20 needs to be changed before the photoresist level reaches the bottom tip of the tubing 24 that extends within the bottle so as to prevent air bubbles from going inside the pump 30. For a typical size photoresist bottle, photoresist is wasted since typically about 300 ml of residual photoresist 26 is left in the bottle 20 when changing to a full photoresist bottle. Moreover, for opaque bottles, even more residual photoresist may be wasted since it is difficult to see the photoresist level. This cost of unused photoresist can be substantial for large scale applications, and over an extended period of time.
Another approach is based on a photoresist reservoir 40′ with a controller 42′ connected to two photoresist bottles 20′, as illustrated in FIG. 2. This approach is known as an automated delivery system (ADS) and consumes the photoresist from each bottle until the tip of the respective tubing 24′ within each photoresist bottle 20′ receives air bubbles. This system provides an undisturbed source of photoresist to the pump 30′ by maintaining the photoresist level inside the photoresist reservoir 40′.
There are several drawbacks to this approach. This type of automated delivery system is expensive, and the operating costs can also be high. Even though there is not a concern of the photoresist pump receiving air bubbles, the system is not able to fully consume all of the photoresist from the photoresist bottles. An average wastage is about 200 ml per bottle. Again, this cost can be substantial for large scale applications, and over an extended period of time.
U.S. published patent application no. 2007/0207259 discloses an integrated photolithography chemical delivery system for a track lithography system. The integrated photolithography chemical delivery system includes a buffer vessel adapted to receive a photolithography chemical from a source volume. The integrated photolithography chemical delivery system also includes a photolithography chemical pump connected to the buffer vessel. A flow control valve is a hybrid manual/pneumatic valve adapted to provide control of the flow of photolithography chemicals from a photoresist bottle in an operating mode and to provide a manual shut-off feature in a service mode. A pressure valve is coupled to the photoresist bottle. Even in this integrated photolithography chemical delivery system, residual photoresist is left in the bottle when changing to a full photoresist bottle.